8 research outputs found
Fermi-liquid theory for a conductance through an interacting region attached to noninteracting leads
We study the relation between the dc conductance and the transmission through
an interacting region based on the Kubo formalism using the perturbation
analysis in the Coulomb interaction developed by Yamada-Yosida and Shiba. We
find that the contributions of the vertex correction to the dc conductance
disappear at T=0 if the currents are measured in the noninteracting leads.
Consequently, the dc conductance is written in a Landauer-type form using the
transmission coefficient for single-particle-like excitation at the Fermi
energy. The results are generalized to a system with a number of scattering
channels, and may be regarded as an extension of the relation derived by
Fisher-Lee.Comment: text is not changed, 6 PS figures were replaced by 6 EPS figures in
order to prevent the control-D problem of the PS file
Fermi liquid theory for the nonequilibrium Kondo effect at low bias voltages
In this report, we describe a recent development in a Fermi liquid theory for
the Kondo effect in quantum dots under a finite bias voltage . Applying the
microscopic theory of Yamada and Yosida to a nonequilibrium steady state, we
derive the Ward identities for the Keldysh Green's function, and determine the
low-energy behavior of the differential conductance exactly up to terms
of order for the symmetric Anderson model. These results are deduced
from the fact that the Green's function at the impurity site is a functional of
a nonequilibrium distribution , which at
coincides with the Fermi function. Furthermore, we provide an alternative
description of the low-energy properties using a renormalized perturbation
theory (RPT). In the nonequilibrium state the unperturbed part of the RPT is
determined by the renormalized free quasiparticles, the distribution function
of which is given by . The residual interaction between
the quasiparticles , which is defined by the full vertex part at
zero frequencies, is taken into account by an expansion in the power series of
. We also discuss the application of the RPT to a high-bias
region beyond the Fermi-liquid regime.Comment: 8 pages, to appear in a special edition of JPSJ "Kondo Effect -- 40
Years after the Discovery", typos are correcte
Out-of-equilibrium Anderson model at high and low bias voltages
We study the high- and low-voltage properties of the out-of-equilibrium
Anderson model for quantum dots, using a functional method in the Keldysh
formalism. The Green's function at the impurity site can be regarded as a
functional of a nonequilibrium distribution function. The dependence of the
Green's function on the bias voltage V and temperature T arises through the
nonequilibrium distribution function. From this behavior as a functional, it is
shown that the nonequilibrium Green's function at high-voltage limit is
identical to the equilibrium Green's function at high-temperature limit. This
correspondence holds when the couplings of the dot and two leads, at the left
and right, are equal. In the opposite limit, for small eV, the low-energy
behavior of the Green's function can be described by the local Fermi-liquid
theory up to terms of order . These results imply that the correlation
effects due to the Coulomb interaction U can be treated adiabatically in the
two limits, at high and low bias voltages.Comment: 6 pages, 4 figures: to appear in J. Phys. Soc. Jpn. 71, No.12 (2002
Quasi-particle description for the transport through a small interacting system
We study effects of electron correlation on the transport through a small
interacting system connected to reservoirs using an effective Hamiltonian which
describes the free quasi-particles of a Fermi liquid. The effective Hamiltonian
is defined microscopically with the value of the self-energy at .
Specifically, we apply the method to a Hubbard chain of finite size (), and calculate the self-energy within the second order in in
the electron-hole symmetric case. When the couplings between the chain and the
reservoirs on the left and right are small, the conductance for even
decreases with increasing showing a tendency toward a Mott-Hubbard
insulator. This is caused by the off-diagonal element of the self-energy, and
this behavior is qualitatively different from that in the special case examined
in the previous work. We also study the effects of the asymmetry in the two
couplings. While the perfect transmission due to the Kondo resonance occurs for
any odd in the symmetric coupling, the conductance for odd decreases
with increasing in the case of the asymmetric coupling.Comment: 27 pages, RevTeX, 14 figures, to be published in Phys. Rev.